Dichlorobenzenes protonation

Figure 33. Principle of proton-driven uphill transport for dopamine under a countertransport mode. The concentration of the carrier lasalocid A in o-dichlorobenzene was 0.1 M. The feed phase (100 ml) was 10 mM Tris-HCI buffer solution (pH 7.4) containing 1 mM ascorbic acid. The receiving phase (0.5-2.0 ml) was a hydrochloric acid solution (pH 0.5-3.0). The initial dopamine concentration in the feed solution was in the range from 1.00 x 10 to 1.00 x 10 M (reprinted with permission from Anal. Sci. 1996, 12, 333. Copyright 1996 The Japan Society for Analytical Chemistry).

The gas phase isomerisation of o-dichlorobenzene (odCB) was studied over protonic zeolites HZSM5, HMOR, HMAZ, HOFF, HBETA and a pillared clay HPILC. All the catalysts deactivate. The deactivation rate is the highest when dry air is used as carrier gas, and the lowest with nitrogen... 

The shape selectivity in products is evidenced mainly by the mdCB/pdCB ratio at a given conversion (Table 4). The behaviour of HPILC cannot be taken into account since the majority of products are formed by radical mechanism. On the protonic zeolites the isomerisation of dichlorobenzenes follows a consecutive reaction scheme for the main part, and the mdCB/pdCB ratio depends on the odCB conversion. However, this ratio can be modified when limitation to diffusion occurs, and the final product pdCB will be then favoured. 

Since the buckminsterfullerenes and C70 were discovered in 1990, there has been extreme interest in these compounds and their derivatives. The first fulleride radical anion, Cgo, was prepared by bulk electrolysis using tetraphenyl-phosphonium chloride supporting electrolyte in dichlorobenzene [76]. Since there are no protons, the spectrum exhibits only one line. Furthermore, because the spin density is so uniformly distributed in the molecule, HFS from naturally... 

Figure 9.1 Spectrum recorded during the decomposition of a solution of propionyl benzoyl peroxide and iodine in o-dichlorobenzene at 100°C. The numbers in parentheses below the formulas indicate the relative spectrum amplitudes for the underlined protons. Spectrum groups referred to in the text are indicated at the top of the figure. Reprinted with permission from H. R. Ward, Accts. Chem. Res., 5, 18 (1972). Copyright by the American Chemical Society.

Chlorobenzene (three different kinds of protons) o-Dichlorobenzene (two different kinds of protons) p-Dichlorobenzene (all protons are equivalent) ... 

Diprotonated, superelectrophilic intermediates were suggested to be involved in both conversions. Considering protonated aldehydes, benzal-dehyde gives a carboxonium ion that is significantly resonance stabilized and thus unreactive towards aromatic substrates such as o-dichlorobenzene or nitrobenzene. Pyridinecarboxaldehydes, however, show much higher electrophilic reactivities due to their ability to form via TV-protonation the superelectrophile (5, eq 8).10 A similar situation is seen in the hydroxyalkylation reactions of acetyl-substituted arenes. Acetophenone is fully protonated in excess triflic acid, but the resulting carboxonium ion (6) is... 

An organocopper intermediate was detected by Lewin and Cohen in the reaction of / -iodotoluene with copper in a good complexing solvent (184). Analysis of protonated aliquots from a reaction performed in quinoline indicated an accumulation of />-tolylcopper to a maximum of 43% after 95 hours, at which point the iodide was consumed, and then a slow decrease to by dimerization. Other experiments also indicate the formation of an arylcopper compound in Ullmann reactions (127,141, 210). The isolation of deuterated products, presumably from the decomposition of an intermediate organocopper species in deuterated benzene and cyclohexane, suggested decomposition to free radicals (127). Decompositions of certain o-haloarylcopper intermediates by a benzyne mechanism cannot be totally excluded. The formation of a dichlorobenzene and by-products such as dibenzofuran and triphenylene from only the ortho isomer of the chloroiodobenzenes in Ullmann coupling reactions (210)... 

The /nfpr-molecular NOE is mentioned above briefly. It is of course this which makes it desirable to use samples in a solvent without nuclei of high for these experiments. There have, however, been few detailed studies of this effect. (234) A density matrix description (235) has been successfully applied to the effect upon the solute (1,1,2-trichloroethane) protons of irradiating the solvent (Me4Si) resonance (235) and differential effects upon the resonances of the [AB]2 spin system provided by the protons of o-dichlorobenzene have been used to aid the assignment. (236)... 

An early report (560) mentions the use of homonuclear spin tickling to aid the assignment of the lines of an AB spectrum from an oriented molecule. The method has been applied to the 4-proton spectrum from ethylene oxide in EBBA (561) and to the detection and assignment of weak transitions in the proton spectrum of oriented o-dichlorobenzene. (562)... 

Magnetic nonequivalence is not uncommon. The spin systems for both para- and ortho-disubstituted benzene rings are AA XX (or AA BB if the chemical shifts are close). Figure 4-3 illustrates the proton spectrum of 1,2-dichlorobenzene (4-8), which is AA XX and relatively complex. Constraints of a ring frequently convey magnetic nonequivalence, as, for example, in butyrolactone (4-9). Even open-chain systems such as... 

Amino- and amido-functionalized monomers can also be polymerized directly with metal catalysts. Living radical polymerization of 2-(dimethylamino)-ethyl methacrylate (FM-5) was achieved with 1-31 (X = Br)/CuBr/L-29 in dichlorobenzene at 50 °C.314 Its ammonium salt (FM-6) was polymerized from the surface of a cross-linked polystyrene latex with CuBr/ L-l in water at 80 °C to generate hydrophilic shells, although there were no data for polymer molecular weight.248 As described above (section II.C.6), (methacrylamides with at least their amido protons unprotected (FM-7, FM-8, and FM-9) can be polymerized with copper-based systems,117168,217,218 but a further optimization seems to be necessary. 

Experimental orientational data have been obtained from proton NMR spectra of 1,4-difluorobenzene, 1,4-dichlorobenzene, 1,4-diboromobenzene and naphthalene dissolved in several nematic solvents at different tempera-tures. The results indicate a relationship between the sign and magnitude of dielectric anisotropies of the nematic solvents and the temperature dependence of the orientational biaxiality ratio of the solutes dissolved in them. ... 

In the double resonance experiments, the effect of the deuterium nuclear quadrupole transitions on the NMR signal50 or the NQR signal42 of another nucleus is observed. For example, an ingenious method of detecting pure quadrupole transitions by nuclear double resonance was suggested by Schwab and Hahn.50 In their experiment, the quadrupole transitions of deuterium in a 12 percent deuterium-enriched sample of p-dichlorobenzene were excited, and the effect on the proton resonance signal through dipolar cross relaxation was detected. The 35 Cl spins served to establish and monitor an ordered metastable spin state of the protons. 

The proton lineshape test uses chloroform in deuteroacetone typically at concentrations of 3% at or below 400 MHz, and 1% at or above 500 MHz. Older instruments and/or probes of lower sensitivity or observations via outer decoupler coils , may require 10% at 200 MHz and 3% at 500 MHz to prevent noise interfering with measurements close to the baseline. A single scan is collected and the data recorded under conditions of high digital resolution (acquisition time of 16 s ensuring the FID has decayed to zero) and processed without window functions. Don t be tempted to make measurements at the height of the satellites themselves unless these are confirmed by measurement to be 0.55%. Since these arise from protons bound to C, which relax faster than those of the parent line, they may be relatively enhanced should full equilibrium not be established after previous pulses. The test results for a 400 MHz instrument is shown in Fig. 3.66. The traditional test for proton resolution which dates back to the CW era (o-dichlorobenzene in deuteroacetone) is becoming less used nowadays, certainly by instrument manufacturers, and seems destined to pass into NMR history. 

Dichlorobenzenes are commercially synthesized in the consecutive chlorination of benzene in the presence of Lewis acid such as FeCU in liquid phase. Similar to proton-exchanged zeolites, alkali-cation exchanged zeolites can catalyze the chlorination of monochlorobenzene and zeolite catalysts tend to prevent the consecutive reactions. Furthermore, the product ratio of dichlorobenzene is varied that is the selectivity of para-dichlorobenzene ( PDCB) among DCB isomers (para-selectivity) is promoted. The selectivity to para-dichlorobenzene to more than 85 % is achieved at 80.5 wt. % conversion level of chlorobenzene in zeolite K-L catalyzed reaction. The catalyst K-L shows its superiority over conventional homogeneous catalyst, FeCh. 

The aromatic protons of symmetrically ortho-disubstituted benzenes also give a symmetrical AA XX spectrum. An example is <7-dichlorobenzene (Fig. 4.42). 

Depending on the mode of substitution, a symmetrically disubstituted benzene ring can show two, three, or four peaks in the proton-decoupled spectrum. The following drawings illustrate this for the isomers of dichlorobenzene. 

FIGURE 4.15 The proton-decoupled NMR spectra of the three isomers of dichlorobenzene (25 MHz). 

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